The students used a sorting board like this.

They worked in pairs to sort their flash cards into piles. Their teacher gave them a Subtraction Facts I Know chart to keep track of their progress. After several days, the students discussed their progress.

Self-Check: Subtraction Facts I Know

With your partner, sort your subtraction flash cards on the Sorting Flash Cards Board. Use your Subtraction Facts I Know chart to record your progress. All these tools are in your Student Activity Book.